This invention relates to a heat reflecting glass plate particularly suitable for use as a vehicle window glass, and more particularly to a glass plate having a heat reflecting multilayer coating which includes a layer of a heat reflective and corrosion resistant metal and several layers of light transmitting metal compound layers.
To produce a heat insulating glass low in transmittance for solar radiation it is well known to use a coating film of silver which is high in infrared reflectance. However, silver film is low in durability and wear resistance and also in transmittance for visible light. Therefore, when a heat reflecting glass using a silver film is required of relatively high transmittance for visible light as in the case of a vehicle window glass it is usual to form a multilayer coating by providing a transparent metal oxide film on each side of a silver film. However, even though such a measure is taken a heat reflective coating using silver film is practicable only in laminated glass since silver is poor in moisture resistance and weather resistance.
To provide a heat reflecting glass which is high in durability and is not necessarily used as laminated glass, recently there are various proposals of multilayer coatings using a heat reflective metal other than silver or a metal nitride. As a heat reflective coating of relatively simple structure, JP-A 61-55603 shows a two-layer coating consisting of a Ti, Cr, Co or Ni film coated on a glass surface and a TiN film covering the metal film, and JP-A 63-242948 shows a three-layer coating made up of a film of a metal such as Ti, Zr, Cr, Ni, Ta or stainless steel coated on a glass surface, a TiN or TaN film formed on the metal film and a metal oxide film as the outermost layer. However, heat reflecting glasses according to these publications are relatively high in reflectance for visible light incident on the uncoated side and are not fully satisfactory in the strength of adhesion of the coating or in wear resistance of the coating, and hence it is difficult to employ either of these proposals in a simple (not laminated) glass plate such as, for example, a window glass for an automobile door window or side window.
JP-A 63-206333 shows a heat reflecting glass with a multilayer coating which is, for example, made up of a TiO.sub.2 film deposited on the glass surface, a TiN film on the oxide film, a TiO.sub.2 film on the nitride film and a SiO.sub.2 film as the outermost layer. JP-A 64-5930 shows a heat reflecing glass high in transmittance for visible light, which has a multilayer coating made up of, for example, a SnO.sub.2 film on the glass surface, a TiO.sub.2 film as the second layer, a TiN film as the third layer, a TiO.sub.2 film as the fourth layer, and a SnO.sub.2 layer as the fifth layer which may optionally be covered with a protective SiO.sub.2 film. The coatings according to these proposals include no metal film. Therefore, to make either of these multilayer coatings comparable to a heat reflective coating using a metal film it is necessary to form relatively thick films of TiN and TiO.sub.2 and this is unfavorable for productivity. Besides, the adhesion of the nitride film to the oxide films is not always sufficiently strong. As the outermost protective layer the SiO.sub.2 film is excellent in durability and transparency. However, to form a SiO.sub.2 film it is necessary to employ either a RF sputtering method which entails high cost of equipment or a sol-gel method which is relatively low in productivity and is liable to suffer from deposition of dust or degradation of quality by drying at high temperature.